It is recommended in the TKA operation to balance the tension of soft tissues to make the rectangular gap in both flexion and extension because significant imbalance may result in eccentric stress on the polyethylene insert. However, no intensive research has been done on the medial and lateral laxity of the normal knee

X-ray of 50 normal knees were taken under the varus or valgus stress in both extension and flexion at 80 degrees. The angle of lines on the femoral condyles and tibia plateau was measured. The same methods were also done for the 20 osteoarthritis knees.

In extension of the normal knees, the mean angle was 5.06 degrees in varus stress and was 2.46 degrees in valgus stress. In flexion of the normal knees, the mean angle was 5.04 degrees in varus stress and was 1.82 degrees in valgus stress. Therefore, the lateral laxity was significantly larger than the medial laxity in both extension and flexion (p< 0.0001). The lateral laxity was significantly larger also in osteoarthritis knees (p< 0.0001).

There are some arguments about the priority to make the perfect rectangular gaps. The methods to measure the tension of soft tissues during the operation are not accurate and does not always reflect the post-operative tensions. Furthermore, the tension during the operation may be different from dynamic phase such as walking and standing. The present study showed that the mediolateral laxity was asymmetrical in the normal knees. This imbalance may be necessary for the medial pivot movement of the normal knee. These results suggest that a slight lateral laxity is acceptable during TKA operation and may be beneficial to achieve the normal kinematics especially for the cruciate retaining prosthesis.

Minimally invasive surgery (MIS) for unicompartmental knee arthroplasty (UKA) has become increasingly popular. However, wound problems may be encountered with longitudinal skin incisions. This probably occurs because the skin is under excessively high tension during MIS. We have been using transverse incisions for MIS-UKA. We describe the surgical technique and an experimental study for assessing blood flow in the skin around the knee.

A 5–7 cm transverse skin incision was made from the medial edge of the patella at the level of 1–2 cm proximal to the joint line. The capsule was incised along the medial parapatellar up to the proximal two-thirds of the patella, and a few cm were also cut along the distal end of the vastus medialis. Because skin on the anterior aspect of the knee is more flexible in the longitudinal direction, exposure is easy even with a small incision.

Experimental study: We measured the direction of blood flow on the anterior aspect of the knee using laser flowmetry. Nine normal subjects were examined. A probe was attached to the skin on the medial parapatellar region, and two 7 cm long parallel depressors were applied bilaterally on the sides of the probe. The depressors were placed longitudinally or transversely under 30N of compression force, and then blood flow was recorded.

Blood flow was markedly increased due to congestion when the depressor was placed longitudinally. On the contrary, changes in blood flow were significantly lower when the depressor was placed transversely.

Transverse incision can lead to better exposure and permit an smaller incision. Moreover, transverse incisions are less invasive to the skin’s circulation and leave less distinctive scars than longitudinal incisions.

Kinematics of mobile bearing TKA has been evaluated by fluoroscopic studies. However, these studies focused on the relative motion between the femoral component and the tibial tray. The purpose of this study was to investigate the kinematics of the polyethylene insert in mobile bearing TKA under dynamic conditions using a custom-made 6-DOF kneesimulator.

The mobile bearing TKA used in this study had a ågstopåh on the tibial tray, allowing rotation and translation. The implants were mounted on the knee simulator. Vertical load and 5-DOF motions were regulated according to the kinematic data from the literature. The knee simulating test was conducted under three different conditions including a static condition and dynamic conditions of 0.5 Hz and 1.0 Hz. Four metal balls mounted on the insert were observed with two cameras, and position of the insert was calculated. Contact pressure on the insert was also measured using a tactile sensor.

Under the static condition, the femoral component kept almostfull contact with the insert. However, the insert shifted posteriorly with impingement to the stop under the 0.5 Hz condition. Under the 1.0 Hzcondition, antero-posterior translation of the insert was larger with impingement to the stop in both directions and contact pressure was greater.

To our knowledge, no study on the motion of the insert of the mobile bearing TKA has been reported. In the present study, the insert showed different motion and contact stress according to the given condition, in spite of the same relative motion between the femoral component and the tibial tray.

We have previously developed a radiographic technique, the oblique posterior condylar view, for assessment of the posterior aspect of the femoral condyles after total knee arthroplasty. The purpose of this study was to confirm the validity of this radiographic view based upon intra-operative findings at revision total knee arthroplasty. Lateral and oblique posterior condylar views were performed for 11 knees prior to revision total knee arthroplasty, and radiolucent lines or osteolysis of the posterior aspect of the femoral condyles were identified. These findings were compared with the intra-operative appearance of the posterior aspects of the femoral condyles. Statistical analysis showed that sensitivity and efficacy were significantly better for the oblique posterior condylar than the lateral view. This method can, therefore, be considered as suitable for routine follow-up radiographs of the femoral component and in the pre-operative planning of revision surgery.

We measured the contact areas and contact stresses at the post-cam mechanism of a posterior-stabilised total knee arthroplasty when a posterior force of 500 N was applied to the Kirschner Performance, Scorpio Superflex, NexGen LPS Flex Fixed, and NexGen LPS Flex Mobile knee systems. Measurements were made at 90°, 120°, and 150° of flexion both in neutral rotation and 10° of internal rotation of the tibial component. Peak contact stresses at 90°, 120°, and 150° were 24.0, 33.9, and 28.8 MPa, respectively, for the Kirschner; 26.0, 32.4, and 22.1 MPa, respectively, for the Scorpio; and 34.1, 31.5, and 32.5 MPa, respectively, for the NexGen LPS Flex Fixed. With an internally rotated tibia, the contact stress increased significantly with all the fixed-bearing arthroplasties but not with the NexGen LPS Flex Mobile arthroplasty. The post-cam design should be modified in order to provide a larger contact area whilst avoiding any impingement and edge loading.

Polyethylene wear in total knee arthroplasty (TKA) is a complex and mutifactorial process. It is generally recognized that wear is directly related to a material wear factor, contact stress, and sliding distance. Conventional methods of predicting polyethylene wear in TKA mainly focus on peak contact stress or subsurface shear stress using finite element method analysis. By incorporating kinematics and contact stress, a new predictor for polyethylene wear in TKA (“Wear Index”) has been developed. The Wear Index was defined by multiplying deformation by femoro-tibial sliding velocity. The purpose of this study was to determine the predictive value of the Wear Index for polyethylene wear in TKA using both a numeric and an in vitro model.

Four commercially available total knee prostheses were modeled for this study. Deformation and sliding velocity were calculated based on the three-dimensional geometry of the components and the gait kinematic inputs using Hertz’s formula. One specimen of each of the four types of total knee prostheses was mounted on a custom-designed knee simulator. Vertical loads and flexion-extension uni-axial motion were simulated using computer controlled servohydraulic actuators. The same gait kinematic inputs used in the theoretical study were used in the simulation test. After the simulations, the surface of the tibial insert was examined microscopically and macroscopically and compared with the theoretically generated Wear Index.

This study showed a high correlation between the numeric model and the simulation. The depth of wear on the tibial insert correlated significantly with the Wear Index. Microscopic findings also demonstrated a good correlation between the Wear Index and observed wear patterns. Sliding velocity is an important factor for understanding wear in TKA. In conclusion, this study suggests that the Wear Index is a reliable predictor of polyethylene wear in TKA, as it incorporates both contact stress and kinematics in its calculation.

We evaluated the geometry of the resected femoral surface according to the theory for total knee arthroplasty (TKA) using three-dimensional computed tomography (3D CT).

The 3D CT scans were performed in 44 knees indicated as requiring total knee arthroplasty. The 3D images of the femurs were clipped according to the following procedures. The distal femur was cut perpendicular to the mechanical axis at 10 mm proximal from the medial condyle. Rotational alignment was fixed at 3 degrees external rotation from the posterior condylar line. The anterior condyle was resected using the anterior cortex as the reference point. The posterior condyle was cut at 10 mm anterior from the medial posterior condyle.

The medial-lateral (ML) width/anterior-posterior (AP) length was 1.58 ± 0.14 (mean ± SD). AP length of the 3D images tended to be longer than the box length of the three kinds of components provided when the ML width of the images was approximately equal to that of each component. The widths of medial and lateral posterior condyles of the images were 30.1 ± 3.8 mm and 24.8 ± 3.0 mm, respectively. In all except one case, the widths of the resected medial posterior condyles were greater than those of the medial condyles of all components when those of resected lateral posterior condyles were equal to those of the lateral condyles of the components.

The shapes of the resected femoral surface did not always match those of the components. The configuration of Japanese knee joints is different from that of American knee joints. Components with appropriate geometry should be designed for Japanese patients.

Flexion after total knee arthroplasty (TKA) has recently been improved by changing implant designs, surgical techniques and early postoperative rehabilitation protocols. Especially for Asian people, deep knee flexion is essential because of their life style. Small numbers of patients can achieve full flexion after TKA, however, most current prostheses are not designed to allow deep knee flexion safely. Furthermore, the kinematics involved in knee flexion greater than 90 degrees in cases of TKA is still unknown, even though fluoroscopic studies have shown the paradoxical anterior femoral translation in posterior cruciate retaining (CR) TKA with knee flexion up to 90 degrees. The purpose of this study was to determine the femoro-tibial contact pattern in deep knee flexion.

The knee that had been operated upon was passively flexed from 90 degrees up to the maximum flexion under anesthesia soon after the surgery. Lateral roentgenograms of the knee were taken during flexion, and the three-dimensional kinematics was analyzed using image-matching techniques. Nine patients with CR type were included.

The average maximum flexion angle was 131.8 °. The contact point moved posteriorly with deep knee flexion except for one patient. Five out of nine patients showed external rotation of the femoral condyle. Two patients showed internal rotation, and the other two exhibited no rotational movement. None of the patients showed dislocation or disengagement of the components. At the maximum flexion, the edge of the posterior flange of the femoral component contacted the polyethylene insert.

This study was performed under non-weight-bearing conditions, but deep knee flexion is not usually performed in weight-bearing conditions. Most of the CR type showed posterior roll back during deep knee flexion. The design of the posterior flange of the femoral component should be changed to prevent damage to the polyethylene.

Introduction: Correct rotational alignment of the femoral component is an important factor for successful total knee arthroplasty. This study evaluated relationship between the transepicondylar axis and the posterior condylar axis in normal, varus, and valgus knees.

Methods: Thirty normal knees (mean age: 66.2 years), 30 osteoarthritic knees with varus deformity (67.9 years), and 25 osteoarthritic knees with valgus deformity (70.7 years) were evaluated using magnetic resonance imaging. Femo-rotibial angle on standing anteroposterior radiograph was 185° in the varus knees and 166.1° in the valgus knees. In the transverse view, the angle between the transepicondylar axis and the posterior condylar axis, and the angle between the line perpendicular to the anteroposterior (AP) axis and the posterior condylar axis were measured in each group.

Results: Transepicondylar line showed 6.4° of external rotation in the normal knees and 6.1 of external rotation in the varus knees relative to the posterior condylar axis. However, transepicondylar axis of the valgus knee showed 11.6° of external rotation. This angle was significantly larger than that of normal knee and varus knee (p < 0.05). The line perpendicular to the AP axis was externally rotated from the posterior condylar axis in 6.3° in the normal knees, 6.6° in the varus knees, and 8.8° in the valgus knees. The external rotational angle in the valgus knees was significantly larger than that of the normal and varus knees (p < 0.05).

Discussion and conclusion: These results suggest that there is no hypoplasia of the posterior part of the medial condyle in varus knees, however, posterior part of the lateral condyle in valgus knee is severely distorted. Based on the results of this study, 3 to 5 degrees of external rotation relative to the posterior condyles is not large enough to achieve correct rotational alignment for valgus knees.

Introduction: Analyses of the 3-D kinematics of TKA in vivo using the x-ray image matching techniques have been widely reported. However, the accuracy of those techniques has seemed not to be discussed enough. To demonstrate more accurate technique for those analyses, we developed the new calibration flame to detect the geometry of the x-ray source and more accurate image matching methods.

Materials and methods: A calibration flame was composed of four ball bearing markers. First, the optimal distributions of those ball markers were determined by computer simulations, and then, using the high-resolutional computed radiography (CR) of a metallic ball taken with the obtained optimal calibration flame, the resolving power of three degrees of freedom (DOF) translations were calculated. Next, the computer-synthesized projected images of the femoral component of TKA were calculated using the estimated x-ray source geometry and experimentally measured geometric data of the prosthesis when the full six DOF poses of the prosthesis were calculated. Matching the computer-synthesized images with the extracted and binalized 2-D CR images of the prosthesis was done automatically using computer in order to minimize the exclusive OR (XOR).

Results: The geometry of the x-ray source was estimated with accuracy of below 0.5 mm in computer simulations. The CR images of the prosthesis were matched with the computer-synthesized images until the XOR reached under one pixel and then, the accuracy of below 1.0 mm translations and 1.0 degrees rotation were recognized for the resolving power of six DOF poses of the prosthesis.

Discussion: The more accurate measurement of full six DOF poses is indispensable to estimate not only the 3-D kinematics but also the contact stresses or predicted polyethylene wear on TKA in vivo. The new calibration flame and the image matching technique we developed appear to be effective for analyses of TKA in vivo.

Our study evaluated the accuracy of an image-guided total knee replacement system based on CT with regard to preparation of the femoral and tibial bone using nine limbs from five cadavers. The accuracy was assessed by direct measurement using an extramedullary alignment rod without radiographs.

The mean angular errors of the femur and tibia, which represent angular gaps from the real mechanical axis in the coronal plane, were 0.3° and 1.1°, respectively. The CT-based system, provided almost perfect alignment of the femoral component with less than 1° of error and excellent alignment with less than 3° of error for the tibial component. Our results suggest that standardisation of knee replacement by the use of this system will lead to improved long-term survival of total knee arthroplasty.

Vascularized bone grafts (VFG) have brought great benefits in the field of reconstruction of the lower extremity. However, complications such as fracture of the grafted fibula and delayed union are sometimes seen. Not only to prevent these complications but also for stability after fracture of the grafted fibula, the Ilizarov external fixator is a very useful option. We report here the clinical results of cases treated by VFG combined with Ilizarov external fixator for reconstruction of the lower extremity.

We have performed 53 vascularized fibula transfers to reconstruct lower extremities. An Ilizarov external fixator was used for the initial immobilization in 7 (2 femur, 5 tibia) and for delayed union or fracture of the grafted fibula in 2 cases of congenital pseudoarthrosis of the tibia.

All patients achieved good bone reconstruction. All are able to walk without a brace except for one congenital case. The average period to achieve bony fusion was 13 months in femur cases, 6 months in adult tibia cases and 2 months in congenital cases. The average periods to walk without a brace were 14 months, 8 months and 10 months respectively. However, it took 9 months and 28 months to achieve bony union in the cases with delayed union or fracture of the grafted fibula.

In the reconstruction of the lower extremities using VFG, the determining factor in method selection is whether sufficient mechanical support is available. An Ilizarov external fixator for immobilization permits the patient to walk as soon as possible. Dynamization from this semi-rigid external fixator causes bone hypertrophy and improved incorporation of the graft.

Our study describes the mid-term clinical results of the use of transtrochanteric valgus osteotomy (TVO) for the treatment of osteoarthritis of the hip secondary to acetabular dysplasia. The operation included valgus displacement at the level of the lesser trochanter, and lateral displacement of the greater trochanter by inserting a wedge of bone. We reviewed 70 hips. The mean age of the patients at operation was 44 years (14 to 59). Most (90%) had advanced osteoarthritis.

The scores for pain and gait had improved significantly at a mean follow-up of 9.4 years. The rate of survival until an endpoint of a further operation during a follow-up of ten years was 82%. The survival rate was 95% in patients with unilateral involvement who were less than 50 years of age at operation. TVO is a useful form of treatment for advanced osteoarthritis of the hip, particularly in young patients with unilateral disease.

The use of standing radiographs to determine correction angles for high tibial osteotomy is not appropriate because the relative angle of the articular surfaces (condylar-plateau angle) in the weight-bearing knee changes after the osteotomy. This may give unpredictable results postoperatively. We found that the condylar-plateau angle in postoperative standing films is very similar to that seen in non-weight-bearing supine views, and suggest that these latter radiographs be used for pre-operative planning. We describe our early results, using a special osteotomy jig, in 140 knees.